The present invention relates to a machine for packaging products in wrappers of sheet material.
The present invention finds application in cigarette packers and in cartoners, by which groups of cigarettes and groups of packets of cigarettes, respectively, are enveloped in sheets or blanks of paper material.
Similarly, the present invention finds application in cellophaners, or overwrapping machines generally, by which packets of cigarettes or groups of packets are enveloped in sheets of thermoplastic material.
Cigarette packers and cartoners typically comprise a wrapping unit equipped with folding devices, designed to envelop packets and cartons in wrappers generally of parallelepiped geometry.
Similarly, overwrappers and cellophaners comprise a wrapping unit by which a packet or a group of packets is enveloped in a sheet of thermoplastic material, in such a way as to cover the four side faces and the two end faces of the aforementioned wrappers with an outer layer of transparent material; the resulting overwrap is then rendered stable by sealing devices positioned to apply a longitudinal seal along one of the side faces and two further seals coinciding with the two end faces.
The machines mentioned above are equipped at the outfeed stage with a conditioning or treatment station where the wrappers are subjected to the application of heat.
The purpose of the treatment in question is to induce a reactivation of hot melt adhesive or to dry an adhesive more quickly, in the case of paper wrappers, or, in the case of overwrapping machines, to induce shrinkage in a covering of thermoplastic material and cause it to hug the packet or group of packets more tightly, thereby eliminating any kinks and creases.
These heat treatment operations are brought about during the passage of the packets or cartons along an outfeed channel created between two mutually opposed branches of a pair of looped belt conveyors.
The aforementioned branches are breasted in contact on one side with two opposite faces of the single wrappers, while sliding in contact on the other side with a source of heat provided by a respective metal plate, heated to a predetermined temperature by electric elements embedded in the selfsame plate.
Machines equipped with the aforementioned heat treatment station betray a serious drawback deriving from high thermal inertia in the metal body of the heated plate, the negative effects of which include, on the one hand, insufficient heat output for the purposes of reactivating or drying an adhesive, or inducing heat shrinkage, and on the other, the risk of wrapping materials being scorched.
An additional drawback derives from the sliding interaction, and consequent frictional contact, between the belt conveyors and the respective heating plates.
Self-evidently, this friction is a cause of wear on the belt conveyors, especially at the high operating speeds typical of modern packaging machines.
The object of the present invention is to provide a machine for packaging products in wrappers of sheet material, such as will be unaffected by the drawbacks mentioned above with reference to the prior art.